Magmatic gases extracted and analysed from ocean floor volcanics

Magmatic gases extracted and analysed from basaltic rocks collected in the FAMOUS area near 36°50′ N in the Atlantic ocean show that the total amount of gas included in the samples varies between about 500 ppm to 1600 ppm. The main gaseous phases included in the various types of basalts consist of CO₂ (270–700 ppm), CO (150–800 ppm), HCl (100–1000 ppm), H₂ (0–50 ppm), SO₂ (up to 175 ppm), N₂ (up to about 213 ppm) and traces of hydrocarbons (up to about 24 ppm). The relative amount of CO, CO₂ and SO₂ varies with both the degree of crystallinity of the rock and with fractional crystallization and/or fractional melting. The glassy margin of pillow lavas have a higher CO/CO₂ ratio than the more crystalline interior. The most fractionated rocks of the series rich in clinopyroxene are depleted in the CO/CO₂ ratio and have a higher SO₂ content than do the most mafic end members rich in olivine. Early-formed olivine was crystallized in a reducing environment rich in CO and H₂ with respect to later formed mineral associations. It is likely that the carbon and sulfur oxidation is taking place at a relatively shallow depth during magmatic ascent or during volcanism. The ocean floor volcanics when compared to subaerial basalts are depleted in SO₂ and have on the average ten times more H₂.